1. Field of the Invention
The present invention relates to apparatus for performing tests on semiconductor devices. More particularly, it relates to probes for making electrical contact with semiconductor devices, and for methods for manufacturing such probes. More specifically, the present invention relates to methods for fabricating members for supporting probe contacts for probes used over a temperature range.
2. Background Art
In the manufacture of semiconductor devices, an electrical test is performed to determine functional performance of the device at the wafer level after all process steps are completed. This test is performed by mechanically contacting the wafer at precise locations on the wafer (known hereinafter as devices or dies). Within the die, specific locations for contacting are also known as interconnect pads. There are two major types of pads, wirebond and C4 (Controlled Collapse Chip Connection).
The current method of performing electrical performance testing in final wafer form is either test a single device at a time or where possible, to decrease cost of test, devices are tested in parallel using a multiplexing system within the tester. This test is performed at several different temperatures to uncover defects that are temperature sensitive. Contacting the device is accomplished by means of a mechanical probe consisting of an upper plate, a probe housing, a lower plate, and a plurality of generally flexible metal probes extending from the lower plate. A space transformer, as described in for example, U.S. Patent Application Publication No. 20060046529 of McKnight et al., may be used to interface the probe to a testing system.
When devices are subjected to a temperature other than what the probe was designed for, i.e. ambient temperature range, and the DUT (Device Under Test) is subjected to a temperature other than this, the DUT in wafer form expands and/or contracts at a rate different than the probe does. If this rate of expansion is greater than the allowable tolerance of the interconnect contact area of the C4 or wire bond pad, the probe will loose electrical contact with the contact area and give erroneous data, indicating that the device has failed when in fact it is potentially a good, working device. There are three major issues which further aggravate this situation:    1. Multi-DUT testing—testing several devices in parallel for cost reductions during test.    2. Temperature extremes changing from −40 to 150° C.    3. Pad geometry shrinking for both wire bond and C4 applications
Multi-DUT sample configurations can be fabricated in many different configurations. One other version not shown is “skip die” where adjacent die are “skipped” to provide adequate trace routing (space transformation) for the interconnection to the test system.
The most common materials used for lower guide plates is Delrin®, a Dupont polymer and Macor® a Corning machinable (alumina) ceramic. Both materials have the advantages and disadvantages. Delrin has good wear properties, low coefficient of friction but has limited temperature range and nearly two times the thermal expansion coefficient of Macor ceramic. Macor ceramic has very wide temperature range of use and about half the thermal expansion characteristics, but is abrasive and must be coated to prevent chafing of the shaft of the probe contacts. The traditional way around this is to build the lower probe die somewhere near the mid temperature range, therefore cutting the error in half.
For a 50 mm die (assuming a multi-DUT application) for 100° C., the thermal offset is about 1.4 mils. That means if the outer probes are off center a maximum of that amount, the minimum offset would be half that amount (0.7 mils), assuming an even expansion rate from the center. If a Multi-DUT probe is used for testing wirebond pad or C4 solder bump and the contact area is relatively small compared to the amount of thermal offset, electrical contact will not be made, and thus the device will be labeled as a fail, and discarded. The other problem with this is it will limit the overall size of the Multi-DUT probe to stay within the contact area. Another method which avoids this problem, is to build separate probe sets for different temperature extremes. This method is costly and lowers throughput on the test system because of the added setup time.